Glucose is reabsorbed in which pa?
**Core Concept**
Glucose reabsorption in the kidneys is a critical process for maintaining glucose homeostasis in the body. The kidneys filter a large amount of glucose from the blood, but most of it is reabsorbed back into the bloodstream in the early part of the proximal convoluted tubule (PCT) to prevent excessive glucose loss in the urine.
**Why the Correct Answer is Right**
Glucose reabsorption occurs through a sodium-glucose cotransporter (SGLT2) in the early PCT. This cotransporter uses the energy from the sodium gradient to transport glucose molecules into the renal tubular cells. Once inside the cells, glucose is either converted to glycogen or released back into the bloodstream. The early PCT is the primary site of glucose reabsorption due to the presence of SGLT2 and the high concentration of glucose in the filtrate at this point.
**Why Each Wrong Option is Incorrect**
**Option B:** The Henle loop is involved in the concentration and dilution of the urine, but it is not the primary site of glucose reabsorption. The Henle loop is divided into the descending and ascending limbs, with the descending limb being permeable to water and the ascending limb being involved in sodium and chloride reabsorption.
**Option C:** The collecting duct is responsible for water reabsorption and electrolyte balance, but it is not involved in glucose reabsorption. The collecting duct is also the site of action for various hormones, such as ADH and aldosterone.
**Option D:** The distal convoluted tubule is involved in calcium reabsorption and fine-tuning of electrolyte balance, but it is not the primary site of glucose reabsorption. The distal convoluted tubule is also the site of action for parathyroid hormone.
**Clinical Pearl / High-Yield Fact**
The kidneys filter approximately 180 grams of glucose per day, but due to efficient reabsorption in the early PCT, only a small amount (about 1-2 grams) is lost in the urine. This highlights the importance of the sodium-glucose cotransporter in maintaining glucose homeostasis.
✓ Correct Answer: A. Early PCT